Process for growing single crystals of sulfides, selenides and tellurides of metals of groups ii and iii of periodic system



L. A. SYSOEV ETAL 3,414,387

SELENIDES AND TELLURIDES OF METALS OF GROUPS II AND Dec. 3, 1968 PROCESS FOR GROWING SINGLE CRYSTALS OF SULFIDES III OF PERIODIC SYSTEM Filed Jan. 5, 1966 United States Patent PROCESS FOR GROWING SINGLE CRYSTALS 0F SULFIDES, SELENIDES AND TELLURIDES OF METALS 0F GROUPS II AND III 0F PERIODIC SYSTEM Leonid Andreevich Sysoev, Ulitsa Krasnoarmeiskaya 12,

kv. Leonid Viktorovich Konvisar, Ulitsa Krasnoznamennaya 7/9, kv. 4; and Emmanuil Kelmanovich Raiskin, Ulitsa Kultury 3, kv. 44, all of Kharkov, U.S.S.R.

Filed Jan. 5, 1966, Ser. No. 518,887 1 Claim. (Cl. 23301) ABSTRACT OF THE DISCLOSURE A process in which single crystals of sulfides, selenides, and tellurides of metals of the Groups II and III, are produced by placing a powder of a sulfide, selenide, or telluride in a graphite container, after which an atmosphere of a gas, which is chemically non-inert towards the crucible material and the single crystal being grown, is charged into the container, the gas being a compound of carbon and the metalloid of the material to be crystallized, after which the container is sealed and the starting material is then melted and cooled to grow a single crystal in the gas atmosphere.

This invention relates to a process for producing single crystals of compounds which tend to dissociate at high temperatures, viz., sulfides, selenides and tellurides of metals of the Groups II and III of the periodic system which are widely used for manufacturing semiconductors, photocells, radiation detectors, ultrasonic amplifiers, etc.

This invention also relates to an arrangement for growing single crystals of compounds that undergo dissociation at high temperatures and for effecting zone purification of said compounds.

Known in the art are vapor-phase techniques for preparing single crystals of sulfides, the vapor-phase zone recrystallization technique being particularly extensively practised.

It is also known to prepare single crystals of sulfides from a melt under an inert gas blanket maintained at a high pressure.

To prepare single crystals, recourse is had to apparatus which makes it possible to move a crucible containing the melt from a high-temperature zone to a zone where the temperature is below the crystallization point. Said apparatus is generally constructed in the form of an autoclave, in which provision is made for displacing the crucible by means of a rod linked to an electric motor.

The vapor-phase techniques for growing single crystals suffer from the disadvantages of requiring a long period to accomplish crystal growth and giving a low yield of single crystals.

When single crystals are grown from a melt under a pressurized inert atmosphere, it is ditficult to obtain sufiiciently pure single crystals, since said crystals are contaminated with a constituent element, viz., a metal present in excess of the stoichiometric ratio.

This disadvantage stems from the fact that graphite elements of the apparatus come into contact with the compounds being crystallized. Said compounds undergo dissociation at high temperatures, so that there take place a reaction between the carbon and the metalloid thus liberated, said reaction involving a reduction in the proportion of the metalloid in the melt and concomitant enrichment of the compound being crystallized with the metal in excess of the stoichiometric ratio. The employment of inert blanketing gases, e.g., argon, neon, nitrogen, etc., only makes it possible to obtain but partial inhibition of said reaction.

Since said technique calls for rapid heating in order to melt the starting material, the heat accumulated by the apparatus elements causes subsequent overheating of the melt obtained.

Crystal growth under high-pressure conditions and crucible displacement require cumbersome and relatively high-power drive motors.

Another disadvantage of said technique is that the necessity of sealing the rod of a substantial diameter may involve inert gas leakage, pressure fluctuations due to said leakage in the course of crystal growth being responsible for a marked deterioration of the quality of the crystals obtained.

Attempts have been made to obviate this disadvantage by placing the drive motor inside of the autoclave inner cavity.

It is an object of the present invention to provide a process for growing stoichiometric single crystals of sulfides, selenides, and tellurides of metals of Groups II and III of the periodic system.

It is another object of the present invention to provide a process wherein the procedure for growing single crystals is made less elaborate and the reliability of the equipment used is enhanced.

It is a further object of the invention to provide an arrangement for growing single crystals according to the present process.

It is a still further object of the invention to eliminate the disadvantages inherent in the prior art methods and apparatus for growing single crystals.

According to the present invention, melting the starting materials and growing the single crystals are accomplished in an atmosphere of a pressurized gas, said gas containing an additive that is non inert both towards the melt and the crucible material.

Said reactive additive consists preferably of a compound formed by the principal constituent element of the crucible material and the metalloid of the single crystal to be grown. Where use is made of a graphite crucible, the additive should be comprised of a compound containing carbon and the metalloid present in the crystal being grown. Thus, growing CdS crystals calls for the employment of an atmosphere of CS Being in a mobile chemical equilibrium with the crucible material and the compound from which crystals are grown, carbon sulfide will promote the preparation of a stoichiometric crystal.

Moreover, the present process makes it possible, if desired, to dope the crystal being grown with a metalloid by carrying out the process of crystal growing exclusively in an atmosphere of the compound formed by the metalloid in question and the crucible material. This doping procedure provides the production of single crystals having the predetermined properties.

The principle of the present invention is disclosed hereinbelow withreference to growing sulfide, selenide and telluride crystals in graphite apparatus.

It will be readily understood by those skilled in the art that this specific embodiment of the invention is indicative of but one of the ways in which the principle of the invention may be employed without deviating from the spirit and scope of the invention.

In the case of growing the single crystals of sulfides, selenides, and tellurides according to the present invention, the effect of chemical interaction between the metalloid of the crystal being grown and graphite is eliminated by incorporating into the atmosphere, in the reaction ves- 3 sel, predetermined amounts of a chemical compound formed of a metalloid and carbon, said compound being carbon sulfide, carbon selenide, or carbon telluride when the crystals to be grown are sulfides, selenides, or tellurides, respectively.

The following examples of preparing the single crystals of sulfides, selenides, and tellurides of the metals of the Groups II and III of the periodic system are presented by way of illustration.

Example l.-Growing of cadium or zinc sulfide single crystals A graphite container is charged with cadmium sulfide (or zinc sulfide) powder and placed in a tubular graphite heater disposed in an autoclave. After sealing the inner cavity, the autoclave is evacuated and heated in order to remove moisture and gaseous admixtures. Into the autoclave is introduced a predetermined amount of carbon sulfide, and then an inert gas is fed from a cylinder into the autoclave to dilute the non-inert additive and bring the pressure in the autoclave to 3040 atm. The subsequent operations include melting the cadmium sulfide charged, somewhat overheating the melt obtained, and thereafter eflecting programmed lowering the temperature of the melt so as to produce a monocrystalline seed in the tapered bottom of the container, said seed undergoing gradual growth from the container bottom upward through the entire volume of the container. Carbon sulfide present in the gaseous phase permits the melt to be overheated as desired, an apropriate temperature gradient being established along the container axis. The overheated starting material undergoes no thermal decomposition, and single crystals having the predetermined characteristics are obtained.

Single crystals of zinc sulfide are prepared by following the procedure disclosed hereinabove.

Example 2.Growing of indium and gallium selenide single crystals Previously prepared indium or gallium sulfide powder is charged into a graphite container and treated as disclosed in Example 1.

Example 3.Growing of cadmium and zinc selenide single crystals Previously prepared cadmium or zinc selenide powder is charged in a graphite container and treated in the same manner as disclosed in Example 1, except that carbon selenide is introduced into the evacuated autoclave.

Example 4.-Growing of indium and gallium selenide single crystals Previously prepared indium or gallium selenide powder is charged into a graphite container and treated in the same manner as disclosed in Example 1, except that carbon selenide is used in place of carbon sulfide.

Example 5.Growing of cadium and zinc telluride single crystals Previously prepared cadmium or zinc telluride powder is charged into a graphite container and treated in the same manner as disclosed in Example 1, except that carbon telluride is introduced into the autoclave.

Example 6.-Growing of indium and gallium telluride single crystals Previously prepared indium or gallium telluride powder is charged into a graphite container and treated in the same manner as disclosed in Example 1, except that carbon telluride is used in place of carbon sulfide.

Example 7.Growing of cadmium and zinc sulfide single crystals Previously prepared cadmium or zinc sulfide powder is charged in a graphite container and treated in the same manner as disclosed in Example 1, except that the blanketing atmosphere in the autoclave consists exclusively of carbon sulfide vapor.

Example 8.-Growing of indium and gallium sulfide single crystals Previously prepared indium or gallium sulfide powder is charged into a graphite container and treated in the same manner as disclosed in Example 1, except that the blanketing atmosphere in the autoclave consists exclusively of carbon sulfide vapor.

Example 9.-Growing of cadmium and zinc selenide single crystals Previously prepared cadmium or Zinc selenide powder is charged into a graphite container and treated in the same manner as disclosed in Example 1, except that the blanketing atmosphere in the autoclave consists exclusively of carbon selenide vapor.

Example 10.Growing of indium and gallium selenide single crystals Previously prepared indium or gallium selenide powder is charged into a graphite container and treated in the same manner as disclosed in Example 1, except that all operations are conducted under a blanketing atmosphere of carbon selenide.

Example 1l.Growing of cadmium and zinc telluride single crystals Previously prepared cadmium or Zinc telluride powder of a stoichiometric composition is charged into a graphite container and treated in the same manner as disclosed in Example 1, except that the blanketing atmosphere in the autoclave consists exclusively of carbon telluride vapor.

Exa rnple 12.Growing of indium and gallium telluride single crystals Previously prepared indium or gallium powder of a stoichiometric composition is charged into a graphite container and treated as disclosed in Example 1, except that all operations are conducted under a blanketing atmosphere of carbon telluride.

The present process for growing single crystals is accomplished in an arrangement which consists of an autoclave, the guiding cavity of said autoclave housing a spring and a reciprocating piston. Said piston is rigidly linked to a container by a rod, while a cord passing through a packing gland connects said piston to an electric motor disposed externally.

Due to these construction features, use can be made of a low-rating electric motor for displacing the container, while improved hermetric seal ensures pressure stability in the autoclave.

It will be readily understood that the embodiment of the present arrangement described hereinabove is indicative of but one effective way of accomplishing the specific process of the present invention, and various modifications in the construction of the arrangement can be practised without deviating from the principle of the arrangement of the present invention.

The present arrangement will become more apparent from the following description and drawings.

FIGS. 1 and 2 are sectional views of two embodiments of the present arrangement.

The cavity of autoclave body 1 (FIG. 1) houses cylindrical graphite heater 2, which provides the desired temperature conditions. A system of shields 3 is intended for effecting thermal insulation of the heater. Container 4 charged with the material being crystallized is rigidly coupled to piston 5, which is mounted in guiding cavity 9. Said piston is supported by coiled spring 6, while a thin metal cord 7 passing through packing gland -8 links the piston to an external electric motor (not shown in FIG. 1). Low-voltage power supply to the heater is effected via the autoclave body and lead 10.

Shown in FIG. 2 is an arrangement intended for use where melt crystallization requires a sharp temperature gradient. Here the container with the material being crystallized is lowered from the heater through a high-temperature zone at the bottom end of the heater into the guiding cavity. Lowering is accomplished by means of the cord, the container being supported by the spring. When the crystallization procedure is carried out repeatedly without breaking the hermetic seal of the autoclave, the container will be reset by the compressed spring.

In situations where melt crystallization should be followed by diminishing gradually the temperature, the guiding cavity may be disposed in the upper part of the apparatus, so that the container will be lowered from the guiding cavity into the heater through the high-temperature zone in the heater top, said lowering being effected by the expanding spring, and the rate of container travel being adjusted by releasing the taut cord.

The present process and arrangement for growing single crystals are distinguished by the following advantages which are conductive to the accomplishment of the objects of the present invention.

(1) The present process and arrangement make possible the production of pure stoichiometric sulfide, selenide, and telluride single crystals or crystals having a predetermined deviation from the stoichiometric proportion.

(2) Performance reliability and constant temperature conditions are obtained due to the fact that the elements of the apparatus do not interact with the metalloid, so that the service life of, for example, a heater is increased by a factor of five.

(3) The present process provides the possibility of overheating the melt of dissociable compounds in such a way that no thermal decomposition of said compounds ensues, thereby making it possible to produce single crystals of better quality.

(4) Due to a small diameter of the cord used (0.2 to 1 mm.), a perfect seal of the cord can be readily obtained, said seal providing constant pressure of the chemically non-inert atmosphere in the autoclave and, therefore, making for favorable conditions for the growth of single crystals.

(5) The employment of a thin cord is instrumental in causing the container to travel smoothly and uniformly 4 at a predetermined rate by means of a miniaturized electric motor (2 w.).

The present invention, therefore, provides a reliable and efficient means of growing stoichiometric single crystals of sulfides, selenides, and tellurides of the metals of the Groups II and III of the periodic system.

The invention likewise provides an arrangement for growing said crystals and effecting zone refining of compounds that undergo decomposition at high temperatures.

It is to be noted that the description of the invention presented hereinabove sets forth only the most practicable and efficient process for accomplishing commercially the principle of the invention, and as it will be readily understood by those skilled in the art, the present invention is not limited by this specific embodiment so that changes can be made without deviating from the spirit and scope of the invention as disclosed in the appended claim.

We claim:

1. A process for growing stoichiometric single crystals of sulfides, selenides, and tellurides of metals of the Groups II and III which comprises placing a sulfide, selem'de, or telluride powder in a graphite container and thereafter charging said container with an atmosphere of a gas which is chemically non-inert towards the crucible material and the single crystal being grown, said gas being a compound of carbon and the metalloid of the material to be crystallized; then sealing said container and melting the starting material, and cooling said material to grow a single crystal in said gas atmosphere.

References Cited UNITED STATES PATENTS 2,890,939 6/ 1959 Ravich 23-3 01 2,947,613 8/ 1960 Reynolds 23273 3,119,778 1/1964 Hamilton 23273 3,188,373 6/1965 Brunet 23273 3,189,419 6 /1965 Wilcox 23-273 3,224,844 12/1965 Gurthsen 23-301 OTHER REFERENCES Zone Melting by Pfann, 1958, by John Wiley & Sons Inc. (pp. and 162), copy in Scientific Library.

NORMAN YUDKOFF, Primary Examiner.

G. P. HINES, Assistant Examiner. 

